create a new folder in resources directory name it “pvp” or whatever you want
create a file __resource.lua

resource_manifest_version '44febabe-d386-4d18-afbe-5e627f4af937'

client_script 'pvp.lua'

create pvp.lua

Citizen.CreateThread(function()
	while true do
		Citizen.Wait(0)
		for i = 0,32 do
			if NetworkIsPlayerActive(i) then
				SetCanAttackFriendly(GetPlayerPed(i), true, true)
				NetworkSetFriendlyFireOption(true)
			end
		end
	end
end)

add start pvp in your server.cfg